The invention relates to methods of making dental models. In particular, the invention relates to methods of making solid dies suitable for preparing composite dental restorations.
In reconstructive dentistry, the construction of dental prosthetics, e.g., inlays, veneers, etc., benefits from being performed outside the mouth. Among other advantages, such an approach reduces patient discomfort, and facilitates manipulation of the restoration during construction.
Previously, this process required several time-consuming steps, and usually required the patient to make several visits to the dentist. Usually on the first visit, an elastomeric impression was taken and a temporary restoration fitted in the prepared tooth. Typically, this elastomeric impression is sent to a commercial dental laboratory for fashioning dies and models (positive replications) from the impression (negative registration). These positive replications are commonly fabricated from dental stones and/or epoxy materials. The commercial laboratory then constructs the dentist-prescribed restoration on the positive replication, and provides the completed restoration to the dentist. These are referred to as "indirect restorations."
On the next visit, the temporary restoration is removed, and the dentist then tries the laboratory fabricated restoration in the patient's prepared tooth to determine form, fit, and suitability of the restoration. If necessary, minor adjustments are made to the restoration, which is then permanently placed in the patient. If minor adjustments by the dentist cannot satisfactorily resolve fit and form problems, the restoration, along with the dies and models are returned to the commercial laboratory for re-make and re-trial, requiring installation of still another temporary restoration. Eventually the restoration is delivered to the patient. Typically, while the laboratory fabrication of dies models and restorations is ongoing, the temporary restoration causes patient inconvenience and discomfort and heightens tooth sensitivity. It would be beneficial to the patient to be able to take an impression, make the requisite dies and models, and fabricate and install a restoration all in a single visit, preferably in a minimum of time.
With respect to building indirect restorations, the ability to isolate the tooth or teeth to be restored by using an extra-oral model of the teeth makes the building process simpler and decreases patient discomfort. For example, ready access to the inlay site is gained and moisture problems are eliminated. Further, fabrication of an indirect restoration permits the dentist or a competent auxiliary technician to more precisely fashion a correct anatomical form for the restoration.
Moreover, modem composite inlay materials are light-curable. Curing such materials is easier outside the mouth. However a common option exercised with indirect resin composite restoratives is additional curing by heat application to the restoration. This is done by placing the light-cured restoration, with or without its attendant die, into a suitable thermostatically-controlled oven for a prescribed period (usually about 10 minutes) at a predetermined temperature (usually about 250.degree. F.). This process effectively "post-cures" the resin composite, thereby improving the composite's physical properties.
Furthermore, a failing of currently available light-cured dental composite resins is the inherent tendency to shrink during polymerization. This shrinkage is invariably toward the source of polymerization initiation, typically a light source when resin composites are placed directly into a prepared tooth. This can result in marginal-gap formation with resultant tendencies for microleakage that can cause tooth sensitivity and potential for dental caries. With indirect, extra-oral polymerization, however, shrinkage occurs on the die/model, so the potential for marginal gapping is minimized.
Therefore, indirect methods permit the manufacture of higher quality restorations, leading to restorations which last longer, again improving patient satisfaction. Success, however, depends on the ability to make accurate and precise models of the teeth to be restored, with a minimum of cost in time and materials.
One type of dental model manufacturing method is described in a brochure from Vivadent USA. This method required use of a heavy viscosity condensation silicone putty as an impression material, and a vinyl siloxane as a modeling material. The modeling material apparently was also highly viscous, since it is described as requiring kneading or spatulating prior to use, presumably to mix the reactive components. Such inferior flow characteristics of the modeling material would also make it difficult to ensure that the impression was completely filled. It is believed that the modeling material was excessively flexible when set, making building of accurate restorations relatively difficult to accomplish. In addition, the use of siloxane impression and modeling materials required use of some additional material to prevent bonding of the materials. In any case, this procedure and the requisite materials proved cumbersome to use, and the system is no longer offered for sale to dentists.
In view of the above considerations, it is clear that existing methods and compositions for making dental models have defects which render them impractical or inconvenient for use. Typically, the compositions require too much handling, and the methods require numerous and complex procedures, thereby preventing completion of the restoration in a single visit, and requiring patients to return on subsequent visits. Conventional modeling materials have also been hard to handle, and suffer from excessive viscosity, rendering accurate modeling difficult.
Accordingly, it is one of the purposes of this invention to overcome the above limitations in the art of making models suitable for preparing dental restorations, by providing a method which is both simple and fast in execution. The method of the invention eliminates complex and time-consuming steps previously required to make dental models, enabling the practitioner to prepare a model, build a restoration, and implant the restoration into the patient in a single visit. A further purpose and advantage of the invention is to avoid the need to send an impression to an external, commercial laboratory for restoration manufacture. The method of the invention enables the dentist or an in-office auxiliary to quickly and easily create dies and models upon which high-quality and durable restorations can be fabricated, while eliminating the need for tooth temporization typically required during conventional indirect restoration fabrication methods, thus avoiding potential problems associated with such temporization procedures.